EP 0 545 230 A1 relates to a method for producing optionally modified oxide ceramic layers on barrier-layer-forming metals and products obtained. To increase the thickness and wear resistance of oxide ceramic layers on barrier-layer-forming metals, a plasma-chemical anodic oxidation is performed in a chloride-free electrolyte bath having a pH value of from 2 to 8 at a constant current density of at least 1 A/dm2 until the voltage reaches a final value. On objects of aluminum or aluminum alloys, an oxide ceramic layer consisting of corundum can be produced. Also on magnesium and titanium, layer thicknesses of up to 150 μm are achieved.
For many applications, highly loaded component parts of valve metals must be corrosion-resistant and wear-resistant even under extreme conditions. This is achieved by providing such objects with an oxide ceramic layer having a wide-meshed interlinked capillary system, introducing particles of fluoropolymers which at least in one dimension are smaller than the diameter of the capillaries, and exposing the object with the prefilled capillary system to changing pressure conditions.
DE 41 24 730 C2 relates to a method for incorporating fluoropolymers into microporous surfaces of objects made of aluminum or its alloys prepared by anodic oxidation, characterized in that an aqueous suspension of fluoropolymers or their precursors having a particle size of from 1 to 50 nm is incorporated into the capillaries of a hard anodized aluminum layer which are perpendicular to the metal.
DE 42 39 391 C2 relates to objects of aluminum, magnesium or titanium having an oxide ceramic layer filled with fluoropolymers, and to methods for preparing them. Described are objects made of the barrier-layer-forming metal having a thin firmly adhering barrier layer on the metal superposed by a sintered dense oxide ceramic layer and, on top of this, an oxide ceramic layer with a wide-meshed interlinked capillary system which is essentially filled with fluoropolymers. In particular, the oxide ceramic layer has a thickness of from 40 to 150 μm. Examples of such objects are rotors for turbo-molecular pumps, turbochargers for diesel or gasoline engines, component parts from vacuum or plasma technology, rollers for coronary discharges, and ultrasonic sonotrodes, each of aluminum or aluminum alloys. It is described that particles of the fluoropolymers or its precursor which are to be introduced into the outer oxide ceramic layer, unless being liquids, are introduced as a solution or suspension in a suitable solvent. The essential core of this description is subjecting the particles of fluoropolymers in a suitable solvent to changing pressure conditions, for which an impregnating system is suitable in which the air is first removed from the capillary system of the oxide ceramic layer using a vacuum, and subsequently, under the action of the vacuum, the particles enter the pores and, after the vacuum has been released, are pressed into pores by the atmospheric pressure and thus are supposed to reach fine ramifications as well.
As particularly suitable fluoropolymers, there are described, in particular, the polymers and copolymers of tetrafluoroethylene, hexafluoropropene, vinylidene fluoride, vinyl fluoride and trifluorochloroethylene. These fluoropolymers are known to be soluble in virtually no solvent, so that it is to be considered that these fluoropolymers are introduced into the surface in the form of dispersions according to DE 42 39 391 C2.
A similar process is described in Japanese Patent JP 2,913,537. A corrosion-resistant construction is characterized in that a plated layer of an Ni—P alloy having a thickness of about 20 μm is provided in an aluminum/alloy part of a turbomolecular pump for releasing chlorine gas in semiconductor production devices, which part comes into contact with chlorine gas, and that a fluororesin protective layer is formed on said plated layer by immersing a rotor and a stator of said turbo-molecular pump into a liquid for forming the layer of fluororesin, followed by drying.
EP 1 485 622 B1 relates to a process for the coating of objects made of valve metals selected from aluminum, magnesium, titanium, niobium and/or zirconium and their alloys with a thin barrier layer consisting of the metal and an oxide ceramic layer provided thereon whose surface has been coated with fluoropolymers, characterized in that the fluoropolymers are introduced into the capillary system of the oxide ceramic layer in the form of a solution by vacuum impregnation, followed by removing the non-wetting portions of the solution and drying.
The above mentioned prior art documents have the common feature that the fluoropolymers are essentially provided on the outer surface of the oxide-ceramic layer, but enter the ramifications only to a low extent.